Let me give a little more information about the experiment.
In this first phase, I would like to see the viability to use Julia to control the satellite attitude (orientation). It is a dynamic language, very different to what we are used to (C/C++). However, it will bring a lot of improvements when developing the attitude control subsystem (ACS) because it will make the gap between the algorithm design and the embedded code smaller. Thus, the proposal is to build a mockup suspended by a thread and control it in one axis using a small reaction wheel. This will provide a very representative example of what will happen in space in terms of controller algorithm. Hence, I will be able to see if this system has the real-time performance required.
If this test is successful, I will apply for funding to build a small Cubesat that the only mission is to test the controller. In this case, there will be a lot of problems, as you said, about temperatures. The space is very extreme. While in Earth’s eclipse, the temperature can go very low. However, while under direct sunlight, it can get very hot. There is an entire field called Thermal Engineering that takes care of those things. They will design a system to ensure that the temperature stays under operational limits. Notice that the lifespan of such missions is very small, usually less than 1 year. Thus, I really do not need to concern about radiation.